INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Growing up in Beverly, Frates – the warrior against ALS who succumbed to the insidious disease in 2019 – was a huge fan of the Bruins’ star and had a poster of the defenseman in his room. — Steve Conroy, Boston Herald, 6 Sep. 2026 But the insidious harm that moves in the other direction — from illness, through a patient, into the person treating her — has no forum at all. — Jennifer Adaeze Okwerekwu, STAT, 1 Sep. 2026 When his insidious nature is revealed, the change in tone and his face gone malformed, the scene feels dynamic in a way that doesn’t require gore or intricate special effects. — Literary Hub, 28 Aug. 2026 The broader opportunity costs of the United States’ Middle Eastern follies are even more insidious. — Emma Ashford, Foreign Affairs, 12 Aug. 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

Many of these migrants navigate the passage on makeshift boats that can capsize in treacherous waters.

— Landon Mion, FOXNews.com, 29 Sep. 2026
The hillside was too treacherous for anybody to carry a litter up it, and a helicopter couldn’t descend in such a narrow airspace.

— Peter Hessler, New Yorker, 28 Sep. 2026

Definition of treacherous

Adjective

In Lepecki’s account, the gesture again demonstrated that stillness in dance always vibrates with subtle motion.

— Sophie Landres, Artforum, 1 Oct. 2026
Against a backdrop of wilting flowers that left a subtle funk in the air, designer Glenn Martens once again put forth ideas that challenged conventions of beautiful clothing.

— Leah Dolan, CNN Money, 30 Sep. 2026

Definition of subtle

Adjective

About 7 in 10 ads carried no AI disclosure, although the count includes uses beyond deceptive impersonations and does not establish how many ads violated a law or misled voters.

— Stefani Langehennig, The Conversation, 30 Sep. 2026
Shrinkflation is particularly confusing, perhaps even deceptive, since sticker prices may remain the same even as the amount of product inside the package quietly falls.

— Sheldon H. Jacobson, Washington Post, 30 Sep. 2026

Definition of deceptive

Adjective

Frankel also faces investment adviser fraud and false-statement counts over SEC filings that allegedly concealed his conviction and a Finra suspension.

— Amanda Gerut, Fortune, 1 Oct. 2026
Klobuchar noted the similarities in Atlanta’s and Iowa’s team names and accused Schmitt of relying on false information to suggest Smith had secretly traveled to Atlanta.

— Claire Carter, The Washington Examiner, 30 Sep. 2026

Definition of false

Adjective

These limitations could easily produce an analysis that is misleading or inaccurate.

— Euan Ashley, STAT, 1 Oct. 2026
As Congress debated the legislation in May 2025, the White House put out a news release with the misleading claim that the One Big Beautiful Bill Act would remove Medicaid coverage for people who are in the country without authorization.

— Phil Galewitz, Miami Herald, 30 Sep. 2026

Definition of misleading

Adjective

Magpies are opportunistic scavengers, incredibly cunning and deceitful and capable of calculated deception.

— Voice of the People, New York Daily News, 28 Sep. 2026
Bogus texts, mystery calls, deceitful emails all aimed at stealing your personal information and your money are relentless.

— Donna Vickroy, Chicago Tribune, 13 Aug. 2026

Definition of deceitful

Adjective

The appropriate level of human involvement depends on financial exposure, customer impact, regulatory requirements, security implications, reversibility and the consequences of an incorrect decision.

— Jayasri Ranganathan, Forbes.com, 29 Sep. 2026
But predictions that the Islamic Republic would collapse proved incorrect.

— Ali Vaez, Foreign Affairs, 29 Sep. 2026

Definition of incorrect

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inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 4 Oct. 2026.

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Synonyms of insidious

adjective

Example Sentences

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